This invention relates to exhaust gas recirculation (EGR) in internal combustion engines, particularly in turbocharged diesel engines.
Controlled engine exhaust gas recirculation is a known technique for reducing oxides of nitrogen in products of combustion that are exhausted from an internal combustion engine to atmosphere. A typical EGR system comprises an EGR valve that is controlled in accordance with engine operating conditions to regulate the amount of engine exhaust gas that is recirculated to the intake flow entering the engine so as to limit the combustion temperature within the engine and hence reduce the formation of oxides of nitrogen. The EGR rate is controlled by controlling the extent of EGR valve opening and the pressure differential across the EGR valve.
Supercharging an engine is one method for improving the performance of a motor vehicle. Supercharging an engine by an exhaust-driven turbine is known as turbocharging. A turbocharger comprises a compressor that boosts intake system pressure and a turbine that is powered by engine exhaust to operate the compressor.
It is believed that turbocharged engines may provide improvements for enabling vehicle manufacturers to achieve both mandated fuel economy requirements and a desired level of engine performance. However, because such engines must also comply with mandated tailpipe emission requirements, it appears that they will still need EGR systems.
When an engine is running supercharged, intake system pressure can exceed exhaust system pressure. Exhaust system pressure that is lower than intake system pressure creates across an EGR valve a pressure differential that is opposite that required for exhaust gas recirculation. Consequently, there is need for a solution that will allow exhaust gas to be recirculated.
It is toward such a solution that the present invention is directed, especially a solution for enabling an engine that has a supercharger, particularly one that has an exhaust gas driven turbocharger, to comply with diverse requirements for fuel economy, tailpipe emissions and engine performance.
Accordingly, the present invention relates to a new and unique EGR system and method for a supercharged engine, particularly a turbocharged diesel engine.
A general aspect of the invention relates to an internal combustion engine that operates with charge air boost and comprises an intake system, an exhaust system comprising a tailpipe, a throttle valve for selectively restricting exhaust gas flow to the tailpipe, and an exhaust gas recirculation (EGR) system for controlled recirculation of exhaust gas from the exhaust system to the intake system comprising an EGR valve having an inlet port communicated to the exhaust system upstream of the throttle valve and an outlet port communicated to the intake system. A control for operating the EGR valve and the throttle valve includes a regulator for operating the throttle valve to partially restrict exhaust gas flow to the tailpipe to regulate the difference between pressure at the EGR valve inlet and pressure at the EGR valve outlet to a desired differential that is substantially unaffected by pressure change in the intake system and in the exhaust system.
Another general aspect relates to a method of exhaust gas recirculation in an internal combustion engine that operates with charge air boost and comprises an intake system, an exhaust system comprising a tailpipe, a throttle valve for selectively restricting exhaust gas flow to the tailpipe, and an exhaust gas recirculation (EGR) system for controlled recirculation of exhaust gas from the exhaust system to the intake system comprising an EGR valve having an inlet port communicated to the exhaust system upstream of the throttle valve and an outlet port communicated to the intake system. The method comprises controlling the EGR valve and the throttle valve, including operating the throttle valve to partially restrict exhaust flow to the tailpipe in a manner that regulates the difference between pressure at the EGR valve inlet and pressure at the EGR valve outlet to a desired differential that is substantially unaffected by pressure change in the intake system and in the exhaust system.
Another aspect relates to a pneumatic regulator for association with an internal combustion engine that has an intake system, an exhaust system including a tailpipe, a throttle valve for selectively restricting exhaust gas low to the tailpipe, and an exhaust gas recirculation (EGR) system for controlled recirculation of exhaust gas from the exhaust system to the intake system including an EGR valve having an inlet port communicated to the exhaust system upstream of the throttle valve and an outlet port communicated to the intake system. The regulator comprises a body comprising pressure differential sensing ports for sensing pressure differential across the inlet and outlet ports of the EGR valve, and a pneumatic pressure regulating mechanism that is associated with a source port adapted to be communicated to a pneumatic power source, with a vent port adapted to be communicated to atmosphere, and with a regulated pressure port, and that operates to develop at the regulated pressure port a regulated pneumatic pressure for operating the throttle valve.
The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention.